The present invention relates to lithography equipment for processing semiconductor wafers.
Step and repeat lithography devices--sometimes called "wafer steppers"--facilitate the mass production of Integrated Circuits (ICs). Typically, this equipment projects an image onto a photosensitive coating of a semiconductor wafer to impart a corresponding pattern. This pattern may be used to selectively etch or deposit material to form desired semiconductor devices. U.S. Pat. No. 5,448,332 to Sakakibara et al.; U.S. Pat. No. 5,286,963 to Torigoe; and U.S. Pat. No. 5,191,200 to Van Der Werf et al. provide representative examples of lithographic equipment used for IC manufacture.
Proper focus is an important aspect of wafer stepper performance. Unfortunately, most conventional focusing schemes are time intensive, complex, and fail to evaluate focus under typical production conditions. As a result, equipment focus variation during production, such as might result from the gradual heating of equipment lenses, is generally not characterized as well as otherwise desired.
Thus, a need exists for a technique to evaluate lithographic equipment that accounts for production conditions in a simple, cost-effective manner. The present invention satisfies this demand and provides other significant advantages and benefits.